Tub support base



FIG. 1 is a top, front, left side perspective view of a tub support base showing my new design, the broken line showing is for illustrative purposes only and forms no part of the claimed design;

FIG. 2 is a rear elevational view thereof, the front elevational view being a mirror image thereto;

FIG. 3 is a right side elevational view thereof, the left side elevational view being a mirror image thereto; and,

FIG. 4 is a bottom plan view thereof, the top plan view being a mirror image thereto. 

The ornamental design for a tub support base, as shown and described. 